Truncated jpeg pictures

I have downloaded some photos onto my PC some weeks ago, I have just got around to looking at them, but they are all truncated. The thumbnails of them look OK. Anyone know how to retify this problem. I have tried opening them in various programs but get the same result. Helppppp.

It might be worthwhile trying another, then run the program and select what you want to view.This is better than just clicking on the picture, and leaving a default to open them, which you may be doing.